I am brand new to the world of Arduino, and am trying to get my brain wrapped around the concept of how to best use a pizeo in a little project that I would like to build. Essentially I want to build an impact sensor that will detect a vibration and immediately respond with a loud chirp. I have looked through the Knock tutorial, and this seems like a reasonable approach for detecting the vibration, but my question is: could I use a single piezo buzzer to both detect the vibration AND issue the subsequent chirp alarm? Not sure how the wiring would look, but hopefully its not too complicated.

On a similar note...how sensitive are the piezo-type sensors to ambient noise vs. physical vibrations; I assume the sensitivity is tunable across a wide range? The build will be in a very loud environment...so I need the piezo to detect a physical vibration/knock and hopefully the sound issued by the piezo will be enough to be heard over the ambient noise...

Hopefully I have not bitten off more than I can chew in terms of my first project; any words of wisdom from folks out there?

could I use a single piezo buzzer to both detect the vibration AND issue the subsequent chirp alarm?

Yes you could, although I am not sure how loud it would be, the sensor is a deaf microphone and a mute speaker. So that might suite you. You need a current limiting series resistor and switch between an analogue input and digital output in your code.

I have chopped up a number of cheapie piezo squeakers to accomplish some really unspectacular results. I finally decided that the piezo diaphragms and the cavities in which they are rigidly mounted are probably acoustically and mass tuned. The more I improved the things the weaker they got. It might be possible to lower the tuned frequency with a drop of mass in the center of the diaphragm.

Every piezo hacker may not have shared this experience, but I gave them up as a bad deal. If you can use the thing exactly as it comes out of the package, it may be good for some kind of off-label use, but given my experience don't expect great things. If I get time to explore some more I plan to utilize automotive sensors and the matching active filter IC that TI, probably among others, makes to condition the output from the transducer.